for a month, john and lisa watched over their son. >> do you remember that moment when they said this appears to be working. >> they came back and said we don't see any leukemia cells and so that was the point of -- i think this is working. i think we're definitely headed down the right path. >> exactly how the treatment works is complicated, but nick is pretty good at explaining it, actually. >> they took out t-cells out of my body and then they engineered them to track down the cancer cells and kill them off. >> did they get them? >> i hope so. upon i'm feeling good now, so i think they did pretty well. >> watch as this gray cancer-killing zealot left attacks the green cancer cell which gets smaller and eventually dies. upon. >> doctors tried this in 59 patients. 25 are now cancer-free. >> our hopes are that eventually we'll, you know, he will be cured that he can kind of put aside this and start moving forward. >> i just want him to be able to enjoy a normal kid's life. >> his biggest thing right now is he is looking forward to getting his learner's permit. >> and soon, instead of